Diff vent

[Schwanger]

Last year our team ran into the problem of how to vent our diff. On the previous we didn't have a problem because the diff housing was a fixed piece (e.g. not rotating) but this car used a rotating housing. I was wondering how other teams accomplished this or if they did like we did and didn't vent it at all.

[Schwanger]

Last year our team ran into the problem of how to vent our diff. On the previous we didn't have a problem because the diff housing was a fixed piece (e.g. not rotating) but this car used a rotating housing. I was wondering how other teams accomplished this or if they did like we did and didn't vent it at all.

[Denny Trimble]

We don't vent it at all, we rely on our shoddy stubshaft bearing seals to equalize pressure.

[Jon Huddleston]

UTA doesn't vent either, probably vents like UW above. So thats where the gear oil keeps coming from! In our Taylor differential we put just enough gear oil to be at the bottom of the bearing seals.

[Schwanger]

We filled ours over half full so I should have been leaking if a seal was bad but it didn't. Maybe if we would have gotten to drive it it would have but that's a whole other story

[drivetrainUW-Platt]

Were with ya schwanger ours didnt do any spinning at comp, we did leak most of our excess oil out of the shaft seals while it sat in the trailer, basically they were trashed from shoving the splines in and out, i would think that the best way to avoid leaks would be to run it pretty low with oil, i mean we are only running for what, 20 miles...Im sure UTA was royally pissed this year and will be runnin a rather "dry" diff in the future http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Ashley Denmead]

Hi Schwanger,

"Parts left off weigh nothing, cost nothing, and don't cause service problems"


http://fsae.com/groupee_common/emoticons/icon_wink.gif

[J. Cheng]

I didn't vent my diff on my last A-Mod at the beginning and oil got out and got onto the rear brake rotors (running inboard brakes). The car blew thru the stop box at an event and didn't want to stop for quite a distance. My solution was to drill a hole in the top part of the bearing carrier which goes into the cavity between the diff support bearing and the stub axle bearing. The hole was then tapped and a small tube fitting was installed with the tube coiled up to prevent water from getting in. My current new car has a similar design except the coil tube is replaced by a tiny sintered bronze muffler, similar to the SSBM, BV or BM series on this page http://www.adsens.net/fpaccessories.htm .

I think all diffs should be vented.

Joe

[Schwanger]

What we had thought about doing but later decided would not be sufficient was to drill a hole in the stub shaft on one side and place a spring and plunger in there so that when the diff heated up the plunger would compress. But I did a quick calculation assuming that the fluid would heat up to something 250 F (I believe a number I found that is said to be the temp at which the fluid breaks down) and the volume expansion was pretty serious.

I totally agree all diffs should be vented.

Brian

[Kevin Hayward]

What sort of temperature does the diff housing reach without the brakes attached to it?

Maybe a single rear disc mounted one side of a LSD causes more headaches than just nasty vehicle dynamics on corner entry.

However if your pressure problem stems from a heat problem maybe the solution is not in better seals but in dealing with either the cause of the heat or trying to dissipate it more effectively. Both of which are valid approaches.

Aluminium cooling fins can be pretty effective. Especially if they are moving through the air pretty quickly.

Sorry to go against the tide and say that I think that not all diffs need to be vented.

Kev

[Schwanger]

We have never gotten to drive the car.

We are using a single inboard brake but the rotor is attached to an aluminum hub and the hub has some kind of thermal isolator between it and the diff housing.

A leak would most certainly stem from an increase in pressure due to the heat created by the LSD.

We were actually going to make a belly pan that had a scoop that would direct air onto the rear brake rotor and the diff, but we ran out of time.

[Charlie]

We've never run a diff vent. We've always had a rotor on the diff; initially it was an aluminum rotor bolted directly to the diff, no isolation of any kind. Those cars had leakage problems, not sure if it related to not being vented or not. They definitely had more than one design flaw, however in 2002 it was still a direct mount and it didn't leak for a few months.

The 2003 and 2004 vehicles had a floating cast iron rotor with aluminum hat. Two very different housing designs, but both Torsens. No leakage problems, no vent.

We fill the diff about 1/3 full, and like Denny said our sideseals probably do a fair job of equalizing pressure.

[Schwanger]

How was your housing built? We just made a cup, basically, and put a large o-ring on the open side that mated with the sprocket and then we made some gaskets to go around bolt holes and the ends of the diff.

[Chuck Maddocks]

what if you filled the diff with oil, ran it for a while around a windy track (so it is actually differenting the torque, producing friction and heat) brought it in, and then (carefully) vented the hot diff. If done correctly, the pressure inside the diff would equalize, but you would still want the air inside to be hot (expanded). plug it up and you shouldn't have to worry about excessive pressure pushing the oil through the seal. this is just an idea. we don't have a rotor bolted directly to our diff so that's less heat. after the diff cools off, there would be a slight vacuum inside the diff (pressure below atm). air might be able to creep in thorugh the seals but you won't have oil coming out while driving the car